What was it all about?

Phytophthora root rot is the most serious and widely distributed disease of avocado worldwide. The causal agent, the soil borne Phytophthora cinnamomi, is a primary constraint on avocado productivity in Australia, destroying the tree root system, and depriving the tree from water and nutrients.

While growers employ integrated management of phytophthora root rot using methods such as effective farm biosecurity, selecting low hazard growing sites, systemic chemicals and adding gypsum, the average yield for avocados across Australian orchards remains low at seven tonnes per hectare, partly due to susceptibility to this disease.

To improve avocado yield, this project employed a novel strategy, RNA silencing, to help obtain avocado rootstocks that are tolerant to Phytophthora root rot.

The team’s report, first published in 2016, established proof of concept for resistant avocado rootstocks of Reed cultivar. The new plants showed active root growth and larger numbers of roots compared with the standard Reed variety. Further, the resistant variety was successfully cloned using the double grafting method.

More work is required to get the new varieties into production nurseries, but the work lays the foundations for a long-term cost effective, environmentally friendly solution to the root rot problem for avocado growers.